Since a liquid crystal display panel can be thinned, lightened and driven with low voltage, the panel has been applied to wrist watches, calculators, personal computers, personal word processors, and the like. However, the color and contrast of a twisted nematic (TN) liquid crystal panel or a super-twisted nematic (STN) liquid crystal panel varies, depending on the direction from which the liquid crystal panel is viewed. In a polymer dispersed liquid crystal (PDLC) panel, liquid crystal molecules are dispersed in a resin matrix between glass substrates to which electrodes are fixed, or a resin matrix is placed in a liquid crystal in a particle or network condition. When voltage is not applied, the liquid crystal molecules are oriented randomly. Hence, there is a difference between the refractive index of the resin and that of the liquid crystal molecules, thus scattering light (FIG. 12A). On the other hand, the liquid crystal molecules orient toward the direction of electric field with the application of voltage, so that the refractive index of the liquid crystal molecules becomes the same as that of the resin and light transmits (FIG. 12B). Therefore, the PDLC panel has high transmissivity and constant color and contrast without being influenced by the direction from which the panel is viewed.
A vacuum deposition method is known as a conventional method of manufacturing a liquid crystal display panel. In this method, glass substrates to which a pair of electrodes are fixed are washed, and a resin seal is then formed on the edge of one substrate (one section of the seal is left open for injection). In order to maintain a predetermined gap, spacers are dispersed on the other substrate. Then, the substrates are fixed to each other, and the resin seal is cured by heating. The panel is placed in a vaccum container in order to keep a vacuum inside the panel. An injection mouth is set in contact with the liquid crystal, and the liquid crystal is then injected into the panel by changing pressure to a normal level.
However, when a highly volatile material is used in the conventional method, the composition of the material changes in the process. Thus, a complex vacuum device is necessary to keep a vacuum inside the panel. It also takes a long time to generate a vacuum condition in the container, so that the productivity of the panels is low.
Conventional methods were proposed which include a method of dropping liquid crystals on a substrate after forming a sealing resin on the substrate and of pressing the resin so as to cure it (Published Unexamined Japanese Patent Application (Kokai) No. Sho 61-190313, Kokai No. Hei 5-5892 and Kokai No. Hei 5-5893), a method of forming a ringed two-layered adhesive seal (Kokai No. Hei 5-5890), a method of dropping liquid crystals in an amount greater than the required amount on one substrate and of sticking substrates to each other in vacuum, while adding pressure to the substrates so as to remove excess liquid crystals through an exhaust section (Kokai No. Hei 6-235925), and a method of coating a mixed material of polymer and liquid crystals on a substrate applied with a sealing material or on another substrate and of carrying out both seal cure and the phase-separation PDLC after adhering the substrates to each other (Kokai No. Hei 4-37820). In Kokai No. Sho 61-190313, the cut surface of the substrates is sealed after pressing the substrates so as to provide a uniform gap. However, excess liquid crystals are liquid and the seal is in an uncured condition, so that the substrates are likely to slide on each other when the seal comes in contact with the liquid crystals. In this invention, on the other hand, the mixed material of liquid crystals and resin is cured when pressure is added to the substrates, so that the substrates do not slide.
In Kokai No. Hei 5-5892, Kokai No. Hei 5-5893 and Kokai No. Hei 5-5890, a pore is formed so as to remove liquid crystals, and a sealing material is cured by adding pressure after removing excess liquid crystals. However, the pore is open when the sealing material is cured, and air bubbles may enter between substrates when pressure is set back to the normal level. The substrates also bulge when pressure returns to the original level, and a precise gap cannot be formed. In this invention, the mixed material between the substrates is cured while pressure is added to the panel, so that no air bubbles enter and a precise gap is formed.
Particularly in Kokai No. Hei 5-5890, air bubbles remain between the first and second seals. In addition, since liquid crystals are liquid, remaining air bubbles enter a display area. However, since the mixed material of liquid crystals and resin is cured in this invention, no air bubbles enter the display area.
Unlike in this invention, the phase-separation of liquid crystals and resin is not carried out while adding pressure to a panel in Kokai No. Hei 4-37820 and Kokai No. Hei 6-235925. In particular, Kokai No. Hei 6-235935 is different from this invention in that the panel is placed in a vaccum.